Investments and Derivative Instruments (Details 9) (USD $) In Millions, unless otherwise specified	Mar. 31, 2012	Dec. 31, 2011
Schedule of Available-for-sale Securities Mortgage Loans [Line Items]
Mortgage Loans	$ 6,275	$ 5,728
Percent of Total	100.00%	100.00%
East North Central [Member]
Schedule of Available-for-sale Securities Mortgage Loans [Line Items]
Mortgage Loans	89	94
Percent of Total	1.40%	1.60%
Middle Atlantic [Member]
Schedule of Available-for-sale Securities Mortgage Loans [Line Items]
Mortgage Loans	501	508
Percent of Total	8.00%	8.90%
Mountain [Member]
Schedule of Available-for-sale Securities Mortgage Loans [Line Items]
Mortgage Loans	125	125
Percent of Total	2.00%	2.20%
New England [Member]
Schedule of Available-for-sale Securities Mortgage Loans [Line Items]
Mortgage Loans	337	294
Percent of Total	5.40%	5.10%
Pacific [Member]
Schedule of Available-for-sale Securities Mortgage Loans [Line Items]
Mortgage Loans	1,850	1,690
Percent of Total	29.50%	29.50%
South Atlantic [Member]
Schedule of Available-for-sale Securities Mortgage Loans [Line Items]
Mortgage Loans	1,443	1,149
Percent of Total	23.00%	20.10%
West North Central [Member]
Schedule of Available-for-sale Securities Mortgage Loans [Line Items]
Mortgage Loans	16	30
Percent of Total	0.30%	0.50%
West South Central [Member]
Schedule of Available-for-sale Securities Mortgage Loans [Line Items]
Mortgage Loans	395	224
Percent of Total	6.30%	3.90%
Other [Member]
Schedule of Available-for-sale Securities Mortgage Loans [Line Items]
Mortgage Loans	$ 1,519	$ 1,614
Percent of Total	24.10%	28.20%